1.1.7 Psychological Factors

What is Physiology in Design?

Physiology is the study of systems and biomechanics within the human body, including their responses, limitations, and capabilities. As designers, understanding physiology helps us create products that work with—rather than against—the natural functioning of the human body. Unlike anthropometrics (which focuses on body dimensions) and ergonomics (which studies human-product interaction), physiology specifically examines how the body functions and what it can and cannot do.

Key Physiological Considerations in Design

As designers, we must understand the physiological limitations that affect how users interact with our products:

1. Visual Accuracy and Color Perception

The human visual system has specific capabilities and limitations:

• Visual acuity: Varies between individuals and decreases with age

• Field of vision: Approximately 120 degrees forward-facing with peripheral vision extending further

• Color perception: Approximately 8% of men and 0.5% of women have some form of color blindness

• Contrast sensitivity: The ability to distinguish between light and dark areas
  

Design implications include:

• Using high contrast for important information

• Not relying solely on color to convey critical information

• Ensuring text is appropriately sized for readability

• Considering lighting conditions that affect visual performance
  

2. Strength and Fatigue

The human musculoskeletal system has specific force-generating capabilities:

• Maximum strength: Varies dramatically based on body position, age, gender, and health

• Sustained force: Much lower than maximum momentary strength

• Fatigue: Progressive reduction in force-generating capability over time

• Recovery time: Period needed to restore full capability after exertion
  

Design implications include:

• Setting appropriate force requirements for controls and mechanisms

• Avoiding designs that require sustained force application

• Creating products that allow for position changes and rest periods

• Considering the reduced strength capabilities of children, elderly users, and those with disabilities
  

3. Muscle Control and Dexterity

The neuromuscular system enables precise movements but has limitations:

• Fine motor control: The ability to make small, precise movements

• Gross motor control: Larger movements involving major muscle groups

• Coordination: The ability to synchronize multiple movements

• Tremor: Small, involuntary movements that increase with age or certain conditions
  

Design implications include:

• Sizing buttons and controls appropriately for human dexterity

• Considering spacing between interactive elements

• Designing for different levels of motor control

• Providing stability features to compensate for tremors
  

4. Hearing Thresholds

The human auditory system has specific capabilities and limitations:

• Frequency range: Typically 20Hz to 20,000Hz, diminishing with age

• Volume sensitivity: Varies across frequencies and between individuals

• Directional hearing: The ability to locate sound sources

• Masking effects: When certain sounds prevent the perception of others
  

Design implications include:

• Using appropriate frequency ranges for auditory feedback

• Providing multiple sensory feedback channels (not just auditory)

• Considering background noise in the use environment

• Designing adjustable volume controls
  

Physiological Considerations in Electronic Systems

When designing products with electronic systems, physiological factors become particularly important:

• Interface designs must account for visual limitations

• Control mechanisms must work within strength and dexterity parameters

• Feedback systems need to consider hearing thresholds and response times

• Electronic displays must account for color perception variations
  

Connecting Physiology to Inclusive Design

Understanding physiological limitations is essential for creating inclusive designs that work for users with different abilities:

• Products can be enhanced with electronic systems to accommodate users with limited strength

• Alternative input methods can be provided for users with different physical capabilities

• Feedback can be designed to use multiple sensory channels

• Adjustable interfaces can accommodate varying visual capabilities
  

Practical Application in Your Design Projects

When applying physiological considerations to your design work:

1. Research the physiological capabilities of your target users

   • Are they children, adults, elderly?

   • Do they have specific physical conditions?

   • What environments will they use the product in?

2. Test with diverse users

   • Observe how different users interact physically with your prototypes

   • Note where they struggle or show signs of fatigue

   • Identify points where sensory limitations affect usability

3. Design with physiological diversity in mind

   • Provide multiple ways to interact with the product

   • Create adjustable interfaces when possible

   • Use appropriate force requirements and control sizes

   • Ensure sensory feedback is perceivable by all users
     

By understanding the physiological capabilities and limitations of your users, you'll create products that are not only more comfortable and efficient but also more inclusive and safer for everyone who uses them.